The present invention relates to seaming equipment for interlocking and sealing the rims of tins, cans and similar metal containers, in particular cans as utilized for foodstuffs.
The prior art of fabricating tin cans and similar metal containers which have a cylindrical body enclosed at each end, has long embraced the practice of fashioning a cylinder from a discrete length of strip metal rolled into a tube and welded along the two butted or overlapping longitudinal edges, then applying a base, filling the resulting container with a given product, and finally capping the open top with a lid. The application of the two end covers, i.e. the base and the lid, is effected in general utilizing seaming techniques well known to those skilled in the art.
In practice, seaming comprises folding the outer edge of the end cover, whether base or lid, and the endmost lip of the cylinder, in such a way that the two interlock.
Further operations may be envisaged, such as the application of a sealing compound to the end pieces in order to render the seam hermetic and obtain a fluid-tight container capable both of preventing any escape of the contents and of disallowing any infiltration of air that would cause the foodstuff to deteriorate rapidly.
Seaming operations currently are effected using a type of machine of which the essential components comprise at least one vertical column, rotatable about its own axis, and a plurality of spindles with respective spring-loaded clamps carried by the column and rotatable both about the column axis and about their own vertical axes.
The differences discernible in such machines lie essentially in the parts used to produce a seaming action; substantially three types of operation are commonly encountered.
A first system utilizes two columns, the first of which used to draw the metal, the second to roll the seam, and is suitable for working metals of thin gage (&gt;0.14 mm approx) and high temper (DR8, DR9 approx), but gives only limited operating speed and poor overlap of the joined edge and lip. In a machine with two columns, moreover, one has the requirement for means by which to transfer the cans from one column to the other.
A second system exploits one column only to effect two rolled seaming passes, though in this instance, difficulties are encountered when working with cans of small diameter, and with the thin gage and high temper metals which tend to be preferred currently by the industry. What is more, the need to operate with small diameter rollers, hence with a localized rather than a continuous compressive force, results in the formation of kinks that necessarily inhibit a thorough compaction of the interlocked seam.
The third system requires two columns and involves two steps both of which are die-seaming operations. In addition to the dimensional drawbacks inherent in such a system, there are those of the machine's complexity in construction and limited operating speed, and worse, its inability to invest the edge and lip with a proper compressive force, applied, that is, from inside the circumference of the seam as well as out, which would improve the seal.
An additional drawback common to all the systems mentioned is the poor interlock between the edge and lip, hence the limited guarantee of a hermetic seal afforded by the finished can.
The object of the present invention is to provide equipment of the type above, capable of carrying out a faultless seaming operation even on cans of small diameter and/or fashioned from thin gage and high temper metals.
A further object of the invention is to provide equipment of compact dimensions able to operate at a rational and high rate of output, and with this end in view, embodied as a single column surrounded by a plurality of work stations.